BANGKOK, THAILAND
— Regional cooperation on policing the Malacca Strait, one of the world's busiest shipping lanes, has led to a sharp fall this year in piracy attacks, cutting the cost of insuring cargo plying its hazardous waters. Crews are now considered less likely to become victims of "maritime muggings" by seaborne assailants.

That's a relief to countries such as Japan and China that depend on Middle East oil imports that transit the 500-mile passageway that snakes between Malaysia, Singapore, and Indonesia. The US also has a stake in securing a commercial choke point that is used by US warships moving between the Pacific and Indian oceans. More than 50,000 ships annually transit the waterway, where half the world's oil passes through.

Still, doubts remain about the continued effectiveness of coordinated naval and aerial patrols to deter criminals that use Indonesia's rugged coastline as cover for attacks on vulnerable vessels. Maritime officials warn that the drop in attacks may be temporary, if patrols aren't maintained, and say that records are incomplete as shipowners don't always report piracy incidents to local authorities.

"The number of attacks has gone down, that's for sure ... [but] the pirates haven't been caught, they're just lying low," says Noel Choong, head of the piracy watch center of the International Maritime Bureau (IMB) in Kuala Lumpur. He says that shipowners are reluctant to report minor piracy incidents as it delays their passage and can add to insurance costs.

According to the IMB's piracy center, just three incidents were reported in the Malacca Strait in the first half of this year, the lowest level since 1999. Far more pirate-prone, based on current data, are the coastlines of Nigeria and Somalia, where attacks are on the increase.

The downward trend in the Malacca Strait began last year, when attempted and actual attacks fell to 18, down from 38 in 2004.

In response to the decline in attacks in the strait, the British-based maritime insurer Lloyd's removed the region from its war-risk insurance category in August, one year after it was put there. This measure had added an extra premium of up to 1 percent of cargo value, infuriating shipping lines.

A new Japanese-led regional initiative to link government databases on maritime security may offer another way to combat the menace of modern-day bluebeards. Eleven countries in Asia have agreed to share information on piracy through a clearing office that opened in September in Singapore, which operates the largest port in the Malacca Strait.

Analysts say this could eventually lead to intelligence sharing and joint prosecutions of crime gangs that exploit the legal gray area of high-seas piracy, though initially the center will focus only on data exchange.

"At least the governments in the region will be sharing information on a regular basis, so let's see what they can do," says Joshua Ho, a senior fellow at Singapore's Institute for Defense and Strategic Studies.

So far, though, neither Indonesia nor Malaysia, which have jurisdiction over much of the Malacca Strait, have ratified the accord, citing concerns over national sovereignty.

And while cooperation by Southeast Asian countries to secure the strait generally is working, much less progress has been made on combating the haze from forest clearance in Indonesia, a seasonal problem that irks neighboring Malaysia and Singapore but has yet to generate any lasting solutions.

In the past, both the US and Japan have proposed sending warships to secure the strait and ensure safe passage, only to be rebuffed by Indonesia and Malaysia. Indonesia argues that it makes more sense to beef up its Navy and Coast Guard, which are often ill-equipped to detect and intercept armed pirates in speedboats. Japan has already helped to finance a modest overhaul of patrol boats.

"The Malacca Strait isn't the only place with piracy issues, but it's always going to be important because it's one of the busiest shipping lanes in the world," says Peter Hinchliffe, general manager of the International Chamber of Shipping in London.

In the strait, keeping merchant cargo safe is only part of the problem. Singapore foiled a terrorist plot in 2002 to hit visiting US naval vessels using a smaller boat rigged with explosives.

Singaporean officials warn that Al Qaeda and its regional allies could also attempt to hijack oil tankers to use as floating weapons against ports, or try to block the strait to commercial traffic. At its narrowest, the waterway is less than two miles across. But most ship owners are focused on the danger posed by pirates. Some have lost crew members to armed attackers who have turned to kidnapping and holding cargo for ransom, as well as regular heists.

And despite the global focus on safeguarding the Malacca Strait for oil tankers and other large vessels, fishing trawlers and other small local craft are more likely to be targeted. Only two of the 18 recorded piracy attacks in 2005 involved large vessels transiting the waterway.